X-ray system for varying intensity x-ray beams



Allg. l5, 1944.' J, LEMPERT 2,355,981

' X-RAY srsTEM FOR VARYING INTENSITY x-RAY .BEAMS Filed Aug. 19, 1942 INVENTOR l JT EM/DEE? ATTORNEY Patented Aug. 15, 1944 X-RAY SYSTEM Westinghouse Fon VARYING TNTENSITY Xfmir. BEAMs l Joseph Lempert, Bloomfield, y

Electric & Manufacturing Com,

pany, East Pittsburgh, Ia.`,`v'vaV corporation of'u vPennsylvania Application Angustia, 194,2,.seria1N0. 455,319 Y The present invention relates to X-ray systems and has particular reference to such av system wherein the quality of the generatedvbeam f of X-rays is varied as desired at any given wattage to produce a radiograph of optimum contrast.

It has long been recognized that sincean' X-ray film or radiograph and a fluoroscopic image are essentially shadow pictures, the quality of the radiograph or image depends `on varying rates of absorption and transmission of X-rays of dilerent materials through which the beam passes. Moreover, the high voltage yshort wavelength X-radiation, commonly called hard X-rays, are the most penetrating; but from the standpoint of contrast on a radiograph or image, it is desirable in many instances to maintain a very appreciable proportion of low `voltage long wavelengthand low penetratingX-radiations called the soft X-rays,

Accordingly, the X-ray tube should have a low ltration in the glass wallsv of the envelope, and the use of filters to filter out low klov'oltage" long wavelength X-r'ays produced yfrom parts of the tube other vthan the focalspot is undesirable from the standpoint of y optimum contrast; Yet the quality of .an X-ray beam is fixed by the wave form of the voltage applied thereto which more or less determines the ratio of the long and short wavelengths of the X-radiations for a given kilovoltage. The use of lters, however, serves not only to cut off more and more `of the low kilovoltage long wavelength or soft X-radiations frequently desired to produce optimum contrast on the resultingradiograph or iluorescent screen, but also decreases the short wavelength X-radiations. Moreovensince such .filters absorb a very large percentage of thelong wavelength X-radiations, a considerable decrease `in the ratio of the long wavelength. to the short wavelength X-radiations results as well as reducing the total X-ray output.

It is accordingly an object of the present invention to provide an X-ray system wherein the ratio of long wavelength X-radiations ,to the short wavelength X-radiations is increased.

Another object of the present vinvention is the provision of an X-ray system wherein-the potential supplied tothe Xray tubeis intermittently varied to'increase` the ratio oflong wavelength X-radiations to the short'wavele'ngth `X-radiations for the .purpose of producing-a radiograph or fluoroscopic image .of optimum contrast.

u Still further Vobjects 'of the-*present invention willbecome obvious to those v'skilled inthe -art by reference tothe accompanying drawing wherein; l l f Fig. 1 is a diagrammatic 'illustratiomof 1an X-ray system showing one embodiment offthe present invention; Y I

Fig. 2 is a graphic illustration showing the distribution curve of an X-ray beam produced by different kilovoltages;

Fig. 3 is a partial diagram of the same circuit arrangement as shown in Fig. 1 but showing a further modification which the present in-` vention may take;

Fig- 4 is a graphic illustration-of thewave' form of the `voltage as produced by the X-ray system as shown `in both Figs. 1 and 3, and

Fig. 5 is a graphic illustration of the customary wave-form of the voltage heretofore pro'- duced in an X-ray system. f

Referring now to the drawing in detail, the system as illustrated in Fig. 1 comprises an energizing transformer 5, the'primary winding 6 of whichis connected to the customary sixty-cycle domestic source of a potential of -230 volts; The high voltage secondary winding 1 is grounded in the center at 8 and one end thereof is connected to the anode and cathode, respectively, of a pair of rectifying rvalve tubes 9 and l0. Similarly, the opposite end of the secondary winding 1 is connected to the anode and cathode, respectively, of a second pair of rectifying valve tubes l2 and I3. A 1f As shown, .the anodes of the rectifying valve tubes l0 and I3` are connected to the cathode of an X-ray tube I4, while the cathodes `of the rectifying valve tubes' 9 and l2 are connected to the anode of the X-ray tube. Since each of the rectifying valve tubes, as well as the X-ray tube, is provided with thermionic cathodes which are heated to an electron-emitting temperature prior to application of energy, aflow voltage transformer l5 is provided from which the rectifying valve tubes 9, I0, and I2 derive their cathode heating energy, with the primary winding of this vtransformer I5 beingconnected to the same source of domestic potential as that of the high tension transformer 5.

vA similar low voltage transformer I6 is provided for supplying heating energy to the cathode ofthe rectifying valve tube I3 with the primary winding thereof being' connected through an adjustable resistance Il to the source of domestic potential. Likewise, a low voltage transformer I8 provides cathode heating energy for the X-ray tube I4 'and it too is connectedthrough an ad Justable resistance I9 tothe same source` of do` so as to be cut out of the circuit and a suitable connectingthe primaryV A, primaries of the transformers switch (not shown) for winding 6 and the I5, I 6 and I8 to the domestic supply source, is closed, a high unidirectional potential will be impressed across the X-ray tube which will havea nects to the remaining elements of the circuit of Fig. 1 at the points 22, 23, 24, and 25, the adjustable resistance is in series with the rectifying valve tube I3 and is thus subjected to high voltage with respect to ground. For this reason it is not as preferable as the arrangement of Fig. 1 since, if adjusted during operation, the control knob should be insulated or grounded so that no danger of high voltage shock will result to the operator.

Adjustment of either the resistance II or the resistance 20 will, as above noted, cause a variasinusoidal wave-form as shown in Fig.v 5 wherein` the ordinate represents kilovoltage and the abscissa time in fractions of the X-ray tube but will follow the sixty cycle frequency of the domestic source ozisupply;`

Moreover, the generated X-ray beam will follow the various curves asshown in Fig.v 2 for the particular kilovoltage applied to the-X-ray tube. From this curve higher the kilovoltage, the higher the intensity of the .short wavelength (hard)- penetrating X-radiations and the greater their ratio to the longer wavelength (soft) low potential X-,radiations over the range of 20 to 50 kilovolts as shown in Fig. 2. The addition of iilters in an eiort to vary the quality of the beam serves only to cutoff more and more of the lower voltage long wavelength A -radiations and in no way increases them so that contrast in the radiograph and, in fact, is decreased ashereinbefore mentioned. l A. j.

In accordance with the .present invention the ratio of the long wavelength X-radiations to the short wavelength X-radiations is increased, thus producing optimum contrast in theradiograph or Iluoroscopic image.l To this end the-potential supplied to the X-ray tube I 4 is varied during one half wave of the valternating current cycle, or one onehundred and twentieth of a second, from the potential supplied` to the X-raytube during the remainingI half wave of vthe rent cycle. Such may be accomplished byA adjustment of the variable resistance II which controlsthe cathode heating current forthe `valve tube I3 as shown in Fig. 1 or by similar adjust-- ment of an adjustable resistance 20 connected in series with the discharge circuit which includes the anode and cathode of the rectifying valve tube I3 asshow'n in the modication of Fig. 3.

By adjustment of the resistance VI 'I the heating current for the rectifying valve ltube I3 is cont'rolled and hence its temperature. Since lthe it obviously follows that the is not improved alternating cur-- a second. Thus-this Y potential will all be in one direction through 'Lil cathode heating temperature can be employed to control thepotential drop across thisirectii-yingl valve tube I3 and the latter Ais operative to pass energy to the X-raytube I4 only during one vhalf wave of the alternating current cycle, thepotential can be varied to any desired-value kfrom that,

ofthe potentialdrop across .the oppositely connec'tedY rectifying valve tubes I0 and I2 which pass energyonly during the remaining half ,wave of the ,alternating current cycleandthe cathode heatingltemperature of which are not adjustable. 1 Ther samey result is obtained by suitable *'ld'l'llst: ment ofthev resistance 20 Vconnected inseriesV with therectifying valve tube I-3 vasi-shown Fig..v 3. However, in this figure, which s hiowsthearrange-r ment of thezvalve ,tubes in the-same way-as thatsgf and, Wh'lliflillusbratvgpurposescons;

tion in the potential supplied to the X-ray tube I4` during one half-wave of the alternating current cycle when the rectifying valve tubes 9 and I3 rare conducting, from the potential supplied to the X-ray tube I 4 during the remaining half wave whenthe rectifying valve tubes I 0 and I2 are conducting energy. Assuming that the transformer-'5 is set so that it would normally supply kilovolts to thev X-ray tube I4 land either the resistance I1 or 20 is adjusted to a kilovoltage of say 40, the potential wave form supplied to the X-ray tube I4 will be as shown in Fig. 4 where againy the ordinate represents kilovoltage and the abscissa time. Y

As shown in Fig. ly during the half wave oi.' the alternating current cycle when the rectifying valve tubes I0 and I2 are conductive, which at the frequency of sixty cycle oi the domestic supply source would be every one one hundred and twentieth of a second, substantially the full potential yof 80 kilovolts .is impressed upon the- X-ray tube. By reference now to Fig. 2, it will be observed that at this high kilovoltageof 80 (which,` although not shown, would be greater than .the 50 kilovolt curve `shown in Fig. 2) the ratiov of the long wavelength X-radiationsto the short wavelength lower voltage X-radiations is one value. During the vremaining half wave of the alternating current cycle when the rectifying valve tubes 9 and I3 are conductive, the potential drops to 40 kilovolts due to the adjustment of the resistance II o-r 20 asv shown in Fig. 4.

.By comparing this latter kilovoltage with the 30 kilovolt distribution curve of Fig. 2, it will be noted that the ratio of the long wavelength X- radiations to the short wavelength X-radiations is of an entirely diiTerent value than it was at the 80 kilovolt cycle, with the lpercentage of the short wavelength high voltage X-radiations being much less than the longer wavelength low voltage X-radiations at 40 kilovolts. Accordingly, during the entire alternating current cycle which includes both the 80 kilovolt and 40 kilovolt X-ray distribution, the ratio of the long wavelength low voltage X-radiations to the short wavelengthV high voltage X-radiations is increased, thus lproducing optimum contrast in the radiograph or liluoroscopic image.

It thus becomes obvious to those skilled'in the art that an X-ray system is herein provided in which' `the potential .supplied to an X-ray tube is intermittently varied during the alternating current cycle to increase the ratio of Ilong wavelength low voltage X-Jradiations to the short wavelength high voltage X-radiations,- thereby producing .optimumwcontra'st in the radiograph. Moreover., the roentgenologist can select any desired vrelationship of. kilovoltages which produceV forhim the optimum contrastdesired.

Although several embodiments. of Athe presentbe made without departing from the spirit and scope of the appended claims.

I claim:

1. An X-ray system for varying the quality of a generated beam of X-rays comprising an X- ray tube, a source of alternating current electrical energy for energizing said tube, rectifying valve tubes for converting the alternating current into unidirectional current prior .to its transmission to said X-ray tube, and means electrically associated with at least one of said valve tubes and operable to cause a variation in the magnitude of the potential passed by the latter during one half wave of the alternating current cycle from the magnitude of the potential passed by the other of said valve tubes during the remaining half Wave of the cycle to cause an increase in the ratio of long Wavelength X-radiations to the short wavelength X-radiations generated by said X-ray tube in order to produce a radiograph of optimum` contrast.

2. An X-ray system for varying the quality of a generated beam of X-rays comprising an X-ray tube, a source of alternating current electrical energy for energizing said tube, rectiiying Valve tubes provided with thermionic cathodes heated to an electron-emitting temperature for converting the alternating current into unidirectional current prior to its transmission to said X-ray tube, and means for varying the current supplied to the thermionic cathode of one of said rectifying valve tubes to cause a variation in the magnitude of the potential passed by the latter during one half Wave of the alternating current cycle from the magnitude of the potential 'passed by the other of said valve tubes during the remaining half Wave of the alternating current cycle to cause an increase in the ratio of long Wavelength X-radiations to the short wavelength X-radiations generated by said X- ray tube in order to produce a radiograph of optimum contrast.

3. An X-ray system for varying the quality of a generated beam of X-rays comprising an X-ray tube, a source of alternating current electrical energy for energizing said tube, rectifying valve tubes provided with -tlnermionic cathodes heated to an electron-emitting temperature for converting the alternating current into unidirectional current prior to its transmission to said X-ray tube, and a rheostat for Varying the current supplied to the thermionic cathode of one of said rectiying valve tubes to cause a variation in the magnitude of the potential passed by the latter during one half Wave of the alternating current cycle from the magnitude of the potential passed by the other of said valve tubes during the remaining half wave of the alternating current cycle to cause an increase in the ratio of long Wavelength X-radiations to the short Wavelength X-radiations generated by said X-ray tube in order to lproduce a radiograph of optimum contrast.

4. An X-ray system for varying the quality of a generated beam of X-rays comprising an X- ray tube, a source of alternating current electrical energy for energizing said tube, rectfying valve tubes for converting the alternating current into undirectional current fprior to its transmission to said X-ray tube, and an impedance device connected in a series circuit with one of said rectiiying valve tubes and operable to vary the magnitude of the potential passed by the latter during one half Wave of the alternating current cycle from the magnitude of the potential passed by the other of said rectifying valve tubes during the remaining half Wave of the alternating current cycle to cause an increase in the ratio of long Wavelength X-radiations to the short Wavelength X-radiations generated by said X-ray tube in order to produce a radiograph of optimum contrast.

5. An X-ray system for varying the quality of a generated beam of X-rays comprising an X- ray tube, a source of alternating current electrical energy for energizing said tube, rectifying valve tubes for `converting the alternating current into unidirectional current Iprior to its transmission to said X-ray tube, and an adjustable resistance connected in series with one of said rectifying valve tubes and operable to vary the magnitude of the potential passed by the latter during one half Wave ofthe alternating current cycle from the magnitude of the potential passed by the other of said rectifying valve tubes during the remaining half wave of the alternating current cycle to cause an increase in the ratio of long Wavelength X-radiations to the short Wavelength X-radiations generated by said X-ray tube in order to -produce a radiograph o optimum contrast.

JOSEPH LEMPERT. 

